Konqueror - Default file manager in KDE3, Konqueror was replaced by Dolphin in KDE4. Very powerful, Konqueror supports profiles, split windows, several view modes, plugins and much more features.
Official website

Krusader - Another powerful file manager for KDE, Krusader has an interface similar to Midnight Commander, starting by default with two panels (the so-called ‘twin panel’ mode).
Official website

Dolphin - The new file manager in KDE4, Dolphin aims to be easy to use and provides basic features for file management. Although the official homepage claims that Dolphin focuses on usability, I found it harder to use than Konqueror or Xfe, for example. But since I don’t use it much, I guess that’s just because I’m not used to it yet.
Official website

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